The "entire" Korean Peninsula could go nuclear if former President Donald Trump returns to the White House, strikes an inadequate nuclear deal with North Korea and pulls out American troops from South Korea, a prominent US expert said Wednesday.

Victor Cha, senior vice president for Asia and Korea chair at the Center for Strategic and International Studies, made the prediction in an article in Foreign Affairs magazine, noting the hope that "reasonable" lawmakers at the Capitol might guide Trump's policies is "misplaced."

In the piece titled, "America's Asian partners are not worried enough about Trump: How his return could destabilize the region," Cha delivered a message to Asian leaders: "The ride is likely to be bumpier and more unpredictable a second time around."

Trump, the presumptive Republican standard-bearer, is set to face off against President Joe Biden in the Nov. 5 general election. The two are set to engage in their first presidential debate Thursday, a showdown that policymakers around the world will carefully watch to hear their policy stances.

"Such a scenario would almost certainly result in the nuclearization of the entire Korean Peninsula," Cha said, claiming that a second Trump term could "most fundamentally" change the Korean Peninsula.

He was referring to the scenario in which Trump cuts a deal with North Korean leader Kim Jong-un that does not disarm the North of short-range ballistic missiles, hypersonic missiles, cruise missiles and tactical nuclear weapons, and then withdraws American forces from Korea.

In the case of South Korea's nuclearization, Cha said a regional chain reaction could ensue.

"Myanmar, for instance, has shown interest in uranium enrichment and in North Korea's nuclear weapons designs," he said. "Although Japan currently embraces nonnuclear norms, the country also has nearly 50 tons of fissile material at its fingertips -- enough to make 5,000 nuclear weapons. Taiwan might not want to be left out of the club."

Concerns have already persisted that if reelected, Trump could threaten to withdraw or scale back the 28,500-strong US Forces Korea in a move to pressure Seoul to jack up its share of the cost for stationing USFK.

Observers sought to assuage the concerns, pointing to congressional efforts to maintain the current USFK troop level through the National Defense Authorization Act.

But this belief is misplaced, Chan warned, saying a second Trump administration is likely to be "far more disruptive" for Asia than the first one was.

"If Trump gets a second chance at the presidency, he is even more likely than before to see allies as trade adversaries, reduce the US military footprint worldwide, befriend autocratic leaders and challenge the norms that have thus far secured nuclear nonproliferation in Asia," he said.

"Washington's Asian security partners will need to become far more self-reliant for their defense as America becomes simply another transactional, self-interested player instead of the benevolent patron that has long supported the liberal order in the region."

Touching on Biden's efforts to reinvigorate alliance-based cooperation in security and other realms, Cha said, "No amount of institutionalization can really Trump-proof these advancements."

The expert also said that China's influence in Asia will "inevitably" grow if the US becomes "just another transactional player" in the region. (Yonhap)